Yarlung and Tsethang are known as the Valley of Tombs and the cradle of Tibetan civilization. The Tibetans believe thy were born of a monkey and an ogress, and Tsethang is the home of the mysterious Monkey Cave. The old earth tombs of the great ancient Tibetan kings, including Songsten Gampo, scatter the plains in the highest royal graveyard in the world. You will also see small but charming temples containing statues of Songten Gampo, his wives and ministers. This area also boasts Tibet's oldest building, constructed in the 2nd century. Yambu Lakhang was built for the first Tibetan king Nyatri Tsenpo and is perched high in the mountains overlooking the plains. Once used as a summer palace by Songsten Gampo, it was converted to a monastery after he moved the capital to Lhasa.